The inventions described below relate the field of automotive air filters and air cleaners for engine air intake systems.
Most people are familiar with air filters used in their cars. These filters are essential to proper operation of the engine, and help extend the life of the engine and its components. Automotive air filters must be replaced periodically because they become clogged and thus inhibit the flow of air into the engine. To the typical consumer, the air filter is cheap, and its replacement is a small additional bother that is handled along with oil changes. However, in high performance applications and in industrial and farming applications, the cost of air filters and the burden of replacement is significant, and a significant increase in filter performance and lifespan can be very valuable.
The air available to the typical automotive or industrial combustion engine always includes some dirt and debris, or particulate material. Particulate material can cause substantial damage to the internal components of the particular combustion system if taken into the engine. The function of the air intake filter is to remove the particulate matter from the intake air, so that clean air is provided to the engine. The intake air stream flows from the influent, or xe2x80x9cdirty,xe2x80x9d side of the filter to the effluent, or xe2x80x9cclean,xe2x80x9d side of the filter, with the air filter extracting the unwanted particles via one or more filter media layers. Filter media are selected to trap particles exceeding a particular size, while remaining substantially permeable to air flow.
The choice of filter media which has a high filter efficiency (that is, it removes a high percentage of the particulate material in the intake air) is important because any particulate matter passing through the filter will harm the engine. The choice of filter media which is permeable to air flow is important because the interposition of the filter into the intake air stream can impede air flow, and this decreases engine efficiency, horsepower, torque, and fuel economy. It is desirable, then, that an air filter effect both a minimal reduction in airflow as well as a minimal increase in the resistance, or restriction, to air flowing into the engine. The choice of filter media which can effectively filter air for extended periods without becoming clogged is also important, so that operation of the engine need not be interrupted frequently to change the air filter.
The features and filter design choices that lead to improvements in one of these parameters can lead to losses in the other performance parameters. Thus, filter design involves trade-offs among features achieving high filter efficiency, and features achieving a high filter capacity and concomitant long filter lifetime. As used herein, filter efficiency is the propensity of the filter media to trap, rather than pass, particulates. Filter capacity is typically defined according to a selected limiting pressure differential across the filter, typically resulting from loading by trapped particulates. For systems of equal efficiency, a longer filter lifetime is typically directly associated with higher capacity, because the more efficiently a filter medium removes particles from a fluid stream, the more rapidly that filter medium approaches the pressure differential indicating the end of the filter medium life.
A particular filter medium can be very efficient, with a single layer removing a large percentage of the particles entrained in the fluid, for example, by collecting particles as a dust cake on the dirty side of the filter. Such xe2x80x9csurface-loadingxe2x80x9d media includes paper and dense mats of cellulose fibers, with small pores. Initially, the dust cake can increase filter efficiency by itself operating as a filter. Over time, the dust cake tends to shorten the media lifetime, as more trapped particles occlude the filter medium surface pores, resulting in increased differential pressure across the filter. Depending upon the airflow through, and operating conditions of, the filter, a high-efficiency surface-loading filter medium can quickly reach a lifetime load. To extend filter lifetime, filter media can be pleated, providing greater filtering surface area.
On the other hand, a particular filter medium can have a relatively low efficiency but high fluid permeability. To provide the desired degree of efficiency, a high-capacity filter may be constructed of a stack, or multiple layers, of lower-efficiency mesh media. Particles that are not trapped by one layer of the filter medium can be removed by an adjacent layer of, or region within, the filter medium. Because the filtration process occurs across the depth, or volume, of the filter, media of this type are designated xe2x80x9cdepth-loadingxe2x80x9d media, and can include foam webs and porous mats of synthetic material.
Depth-loading media can have a substantially uniform density across depth of the media, or can have a varying, gradient density. Uniform-density depth-loading media can be less expensive to produce than gradient-density depth-loading media. However, gradient-density depth-loading media tends to be more efficient. As with a filter constructed of surface-loading media, the lifetime of a depth-loading media can be extended by pleating the filter media. Nevertheless, increasing the thickness of filter media or providing excessive pleating can restrict airflow into the engine.
Currently available air filters balance the various design parameters to achieve the optimal balance of efficiency, flow rate and life span by accepting relatively short life span and single-use embodiments in order to obtain high efficiency and capacity. The deleterious effects of certain harsh operating environments, such as construction sites, long haul operations and off-road, recreational, and sports applications, can lead to degraded efficiency or unacceptably short lifetimes in these air filters, especially under high airflow conditions.
The devices described below provide for an extremely long-lived engine air filter which exhibits high efficiency and high capacity. The filter comprises a fluid filter media and a fluid filter including a porous natural fiber filter media region receiving an influent fluid stream containing particles; and a porous synthetic fiber filter media region in proximate contact, and in fluid communication with, the natural fiber filter media region from which it receives a filtered fluid stream. The natural fiber filter media is formed from pileous, absorbent, and wickable natural fibers, including one or more layers of cotton mesh; and the synthetic fiber filter media region is formed from a pre-selected pileous and absorbent spunbond polyester fiber formed of one or more layers of spunbond polyester fiber.
The natural fiber filter media region traps a first portion of the particles in the influent fluid stream while the influent fluid stream passes substantially unimpaired through the pores, and creates a filtered fluid stream having therein a second portion of the particles. The synthetic fiber filter media region receives the filtered fluid stream and traps a substantial amount of the second portion of particles in the filtered fluid stream, while the filtered fluid stream passes substantially unimpaired through the pores, and releasing a filtered effluent fluid stream. The filter also includes two structural mesh layers with the natural fiber filter media region and the synthetic fiber filter media region being interposed between them. The natural fiber filter media is wetted with a small amount of oil to enhance its efficiency.
The filter may include at least one of a gradient-density natural fiber filter media region, and a gradient-density synthetic fiber filter media region. In the gradient-density natural fiber filter media region, a first cotton mesh layer has a first cotton mesh density, and a second cotton mesh layer has a second cotton mesh density. The first cotton mesh density is less than the second cotton mesh density. Accordingly, the first cotton mesh layer is disposed closer to the receiving of the influent air stream, and the second cotton mesh layer is disposed closer to the filtered effluent air stream. In the gradient-density synthetic fiber filter media region, a first spunbond polyester fiber layer has a first polyester fiber density, and a second spunbond polyester fiber layer has a second polyester fiber density. The first polyester fiber density is less than the second polyester fiber density. Accordingly, the first spunbond polyester fiber layer is disposed closer to the second cotton mesh layer, and the second spunbond polyester fiber layer is disposed closer to the filtered effluent air stream.
In a simple embodiment, the filter comprises several gauze layers and one or two spunbond polyester layers sandwiched between two metal screens. The gauze is a thin, loosely woven cotton cloth having a relatively low thread count (threads per inch). The gauze layers in the filter each have differing thread counts, so that the air flow path through the combined several layers of gauze is tortuous. The polyester layers may also have differing densities. The thread count of the gauze layers increases from the intake side to the output side, as does the density of the polyester layers. In this manner, the gauze layers provide a very efficient filter with a high capacity and low resistance to air flow.